Place stock, porter, mirepoix, and bay leaves in large pot; add hot pepper sauce and thyme sprigs; bring to a boil; reduce heat to medium; simmer 1 hour; remove from heat; strain through fine chinois into another large pot; reserve.

Place clams in large pan with high sides; roast clams in oven until they begin to open and release their juices (about 3 minutes); remove from oven; place clams in a bowl with slotted spoon; reserve (keep warm).